This invention relates to span gauges for measuring the span between thumb and finger holes of a bowling ball and includes means for automatically compensating for the pitch angle of a pre-drilled thumb hole.
When finger holes are made in a bowling ball a thumb hole is first pre-drilled and then the finger holes are measured from the nearest point on the diameter of the thumb hole. This is usually done with a gauge having a curved surface matching the curvature of the bowling ball. Usually these gauges have a fixed tongue for engaging the edge of the thumb hole to position the span gauge for measuring to the finger hole. This fixed tongue however, does not allow adjustment of the span gauge for differences in the pitch angle from one thumb hole in one ball to a different angle thumb hole in another ball. Thus, the curved edge may not mate correctly with the curvature of the ball, thereby creating an error in the measurement. This is a disadvantage because the correct measurement is extremely important to prevent misalignment of the finger holes. This misalignment can not only cause damage to the fingers but also can disturb the aim in the delivery of the ball. Further, once an error has been made in the placement of the finger holes it is difficult if not impossible to correct.